1. Field of the Invention
The present invention relates to a constant velocity joint used for the transmission of rotational torque in a motor vehicle and the like. More particularly, it relates to a constant velocity joint of the cross groove type, wherein the outer and inner joint members have plural guide grooves inclining with respect to their rotational axis in circumferential directions.
2. Discussion of the Prior Art
A constant velocity joint shown in FIG. 8 is know as the cross groove constant velocity joint. The constant velocity joint is composed of an outer joint member 1c, an inner joint member 2c disposed within the outer joint member 1c in a coaxial relationship therewith, plural balls 3c disposed between the outer and inner joint members 1c and 2c, and a cage 4c holding the balls 3. The outer joint member 1c has circumferentially spaced plural first guide grooves 15c extending from one open end of the outer joint member 1c to the other open end thereof. Alternate ones of the first guide grooves incline with respect to the rotational axis of the outer joint member 1c in one circumferential direction, and remaining ones of the first grooves incline with respect to the rotational axis in the opposite circumferential direction. Also, the inner joint member 2c has circumferentially spaced plural second guide grooves 24c extending from one end of the inner joint member 2c to the other end thereof. The second guide grooves 24c are formed at circumferential locations corresponding respectively to the circumferential locations of the first guide grooves 15c, and each of the second grooves 24c inclines with respect to the rotational axis of the inner joint member 2c in a circumferential direction opposite to that of corresponding one of the first guide grooves 15c. The plural balls 3c are disposed between the first guide grooves 15c and the second guide grooves 24c for rolling movement, and are held by windows 45c of the cage 4c.
In a process of producing the outer and inner members 1c and 2c, the first and second guide grooves 15c and 24c are formed using a milling cutter, and their machined guide surfaces are then ground using a grinding wheel having a hemispheric shape.
To grind the first and second guide grooves 15c and 24c accurately, it is required to take into account the pitch diameter of the balls 3c, errors in pitch between every two adjacent guide grooves, errors in pitch between every two alternate guide grooves, the radius of the guide grooves, the contact angle between the balls 3c and the guide grooves, and the like.
However, since the first and second guide grooves 15c and 24c are formed to incline circumferentially, as shown FIGS. 9 and 10, respectively, the both end portions 17c and 26c of the first and second guide grooves 15c and 24c are asymmetric with respect to the center lines L3, L4 of the guide grooves 15c and 24c, respectively. This asymmetry in the shape of the guide groove 15c and 24c causes a problem during the grinding operation. Namely, when the grinding wheel G passes through the end portion 17c of one of the first guide grooves 15c, the contacting area between the grinding wheel G and one side surface Sa of the guide groove 15c is larger than the contacting area between the grinding wheel G and the other side surface Sb of the guide groove 15c, as shown in FIG. 9. This causes the grind wheel to slightly move in a lateral direction perpendicular to the center line L3, the moving locus of the grinding wheel deviating from the center line L3 of the first guide groove 15c. As a result, it becomes difficult to accurately grind the whole area of the first guide grooves 15c, thereby giving a bad influence on rolling movements of the balls 3c after assembly. Above problem also occurs when the second guide grooves 24c are ground.